Reactivity of free N-heterocyclic carbenes in dichloromethane

The reactivity of free 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene ( Me IPr ) and 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene ( IDipp ) in dichloromethane was investigated. Me IPr reacts relatively slowly and selectively with the solvent under the formation of imidazolium salt [ Me IPr H]Cl, which was characterised through NMR and IR spectroscopy as well as single crystal X-ray diffraction. Through deuterium labelling experiments the reaction rate was determined. In contrast IDipp reacts unselectively to various imidazolium salts. Due to the slow decomposition rates of Me IPr and IDipp in CH 2 Cl 2 , reactions of the free carbenes with BeBr 2 to [( Me IPr )BeBr 2 ], [( Me IPr ) 2 BeBr 2 ] and [( IDipp )BeBr 2 ] can be performed. The decomposition rates of 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene and 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene in dichloromethane are slow enough to facilitate reactions with the free carbenes and Lewis acids.